A storage system includes a plurality of storage devices for storing data as well as a storage controller for controlling the storage devices, and is intended to provide high-capacity data storage space to a host computer.
The storage system is required to store a large amount of data at a low cost. In order to satisfy this requirement, there is known a technique that reduces the size of write data received from a host and stores the write data in a storage device. When write data is reduced in size and then stored in the storage device, the data storage costs (the bit cost of the storage medium, the power consumption cost of the storage device, or other costs) can be reduced. In order to reduce the data size, there is a technique that reduces the data size while maintaining the meaning of the data by using a lossless compression algorithm. This process is referred to as “lossless compression” or “compression”.
When data is compressed and stored in a storage device, the overhead of the compression process occurs in writing and the overhead of the decompression process of compressed data occurs in reading, which may result in a reduction in access performance. In other words, the reduction in the amount of stored data and the access performance have a tread off relationship. In order to avoid this, there is a technique that selectively performs data compression. For example, Patent Literature 1 discloses a method that, in a storage system that manages a plurality of storage tiers, reduces the amount of stored data while preventing the reduction in access performance, for example, by compressing and storing data to be moved to a lower tier.
Further, as another technique for reducing the amount of data to be stored, there is also a deduplication technique. For example, when a storage system detects that a plurality of pieces of data having the same content are present in the storage system, the technique leaves one of the pieces of data in a storage device within the storage system, and does not store the remaining data in the storage device. The amount of write data stored in the storage device can be reduced to less than the amount of write data received from the host by using either the deduplication technique or the lossless compression technique. Thus, in a broad sense, it can be said that the deduplication technique is also one of the compression techniques.